Our objective is to identify the host-associated signals that stimulate the spirochetal agent of Lyme disease (Borrelia burgdorferi) to become infective in vector ticks and to determine how dormancy is maintained. The physiological mechanisms that regulate developmental diapause will be compared to those regulating infectivity of other Ixodes-associated pathogens. Toward this end, we shall identify variables that affect the spirochete's ability to become motile in ixodid ticks during the period of contact between vector and reservoir host. Methods for enema and for capillary feeding will be perfected to facilitate discrimination between physical, chemical and endogenous factors as developmental stimuli. In addition, we shall examine related aspects of tick physiology that regulate onset of infectivity of a piroplasm, embryogenesis of a parasitoid wasp and of rapid-engorgement of the host tick. In this manner, we shall explore the conditions that affect motility and dormancy of the Lyme disease spirochete, ultimately seeking to understand how human hosts become infected by this important human pathogen.